1. Technical Field
The embodiments herein generally relate to electrical converter circuits and, more particularly, to utilizing a pulse skipping modulation (PSM) circuits to control a direct current to direct current (DC-DC) converter of an integrated circuit (IC) chip.
2. Description of the Related Art
Various types of electronic equipment, more particularly, portable or handheld electronic devices such as cellular telephones, personal digital assistants (PDAs), etc., are capable of being powered from a self-contained power source such as a battery, which may be recharged by an external power source. Moreover, these devices typically contain an integrated circuit chip(s) embedded in the device. Additionally, some interfaces may provide a power source through an interface itself such as a Universal Serial Bus (USB). A DC-DC converter may be utilized to convert the battery voltage, external voltage, or both voltages to a DC value which will supply power to various circuits of the integrated circuit chip(s). The converted voltage may be a supply voltage (rail voltage) provided to a load. However, because the load at the output of the DC-DC converter may vary substantially, the load current may also vary considerably. Furthermore, in some instances it is desirable for the DC-DC converter to be as efficient as possible in the low power state to extend the device's battery life.
However, when switched DC-DC converters are used, the converters are inherently less efficient when driving light loads because the power needed to switch the large power field-effect-transistors (FETs) is comparable or greater than the energy transferred to the load. Moreover, when driving a heavy load, the energy needed to switch the FETs is less relative to energy transferred to the load, so the efficiency is higher. A conventional technique to improve light load efficiency is to implement a pulse-frequency modulation (PFM) converter, which modulates the frequency that the DC-DC converter operates to optimize efficiency by enabling the power FETs to bring the output voltage level to a high threshold, then disabling the FETs until the voltage drops to a low threshold. This well-known technique improves efficiency by reducing the number of times the FETs are toggled to transfer power to the load.
Typically, the architecture of these PSM converters implements some form of current mode control. However, current mode control is generally difficult because it requires sensing currents, which is difficult to sense due to noise, offsets and circuit complexity. Also, sensing a current typically requires a sensing resistor, which may negatively impact efficiency. Thus, sensing current in a switched DC-DC converter may be difficult to do or may be undesirable. Accordingly, there remains a need for a new DC-DC converter having improved efficiency characteristics at low load current levels.